RFR: 8295851: Do not use ttyLock in BytecodeTracer::trace [v3]

[David Holmes]

On Fri, 20 Jun 2025 13:29:42 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> This didn't need ttyLock for synchronization, the code only needs to see if the method changes so it can print the method name before the bytecodes, like:
>> 
>> [490166] static void java.lang.String.<clinit>()
>> [490166]       13    18  putstatic 613 <java/lang/String.CASE_INSENSITIVE_ORDER:Ljava/util/Comparator;>
>> [490166]       14    21  return
>> 
>> [490166] static void java.lang.System.<clinit>()
>> [490166]       15     0  invokestatic 471 <java/lang/System.registerNatives()V>
>> [490166]       16     3  aconst_null
>> [490166]       17     4  putstatic 474 <java/lang/System.in:Ljava/io/InputStream;>
>> 
>> Verified manually and added some parallelism to the test, and fixed trace() to initialize is_linked(), which it always is.
>> Also ran tier1-4.
>
> Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Put back include osthread.hpp

src/hotspot/share/interpreter/bytecodeTracer.cpp line 182:

> 180: // the method has changed. If this method is redefined and removed, that's ok because the method passed in won't match, and
> 181: // this will print that one.
> 182: static Method* _current_method = nullptr;

And if we are calling `trace_interpreter` from multiple threads they will each stomp on this shared global field. Sorry I can't see how some form of locking is not needed here.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/25915#discussion_r2160763661